Using the Chrome developer tools (or similar) you can figure out the classes that the relevant components belong to. E.g.
sidemenu, etc. If you search the Grafana repo for these keywords, you’ll find the relevant scss files where the styles are defined. Adding
visibility: hidden to the respective definitions will hide the elements.
Note that, rather than editing all the original (s)css files themselves, it would be considered better practice to introduce an additional CSS file that simply overrides the defaults in those existing files. (they’re called cascading stylesheets for a reason )
Another note (and this is not best practice), but if you just want to experiment, you don’t actually need to build from source every time you make CSS changes. You can simply edit and introduce additional CSS into a pre-built tree.